This invention relates generally to an improved breathing method and apparatus for supplying air to a user having a lower partial pressure of oxygen (PO.sub.2) than the ambient air so as to simulate an elevated altitude.
Persons who ordinarily function at a near-sea-level altitude frequently experience headache, shortness of breath, nausea, sleeplessness, and reduced endurance during the initial days at higher altitude, e.g. above 7,500 feet. These factors are, in large part, attributable to the diminishing amount of oxygen available as altitude increases. A typical situation involves a sea-level resident who occasionally takes a skiing weekend above 7,500 feet. As altitude increases, oxygen availability diminishes, thus requiring the person to breathe deeper in an effort to supply sufficient oxygen to his bloodstream. The partial pressure of oxygen (PO.sub.2) at 7,500 feet is only 75% (of the PO.sub.2 at sea level) and at 10,000 feet is only 65%. At 19,000 feet, the PO.sub.2 is only 50%, thus meaning that a unit volume of air at 19,000 feet contains only half as much oxygen as that same unit volume at sea level. Typically, after a few days at the higher altitude, the person will become acclimated and the aforementioned problems subside. Interestingly, evidence suggests that persons who experience high altitudes on a frequent and regular basis appear to maintain a certain degree of acclimation to the altitude and are considerably better able to avoid the aforementioned problems than infrequent visitors.
Applicant's parent application discloses a breathing method and apparatus for enabling a user, while at low altitudes, e.g. sea level, to acclimate himself to high altitude conditions.
In the preferred embodiment disclosed in Applicant's parent application, first ends of inspiratory and expiratory tubes are coupled to a mouth and/or nose breathing mask. The remote end of the expiratory tube is coupled through a proportioning means to the environment and to a reservoir or air storage chamber. The remote end of the inspiratory tube is also coupled to the proportioning means so as to pull ambient air from the environment, as well as oxygen depleted air from the reservoir. By varying the proportioning means, the ratio of ambient air to expired air, and thus the oxygen concentration of the inspired air, is varied so as to enable the user to select a particular elevated altitude to be simulated. In order to accommodate users having different tidal volumes and rates, a large capacity reservoir sufficient to accommodate the largest tidal volume user is provided. Carbon dioxide (CO.sub.2) absorber material is incorporated in the system to remove CO.sub.2 from the air drawn from the reservoir for inspiration by the user.
In use, a person may breathe through the apparatus for approximately 30-60 minutes per day, gradually increasing the elevation of the simulated altitude in increments of 2,000 to 3,000 feet, as he becomes acclimated to each altitude. Evidence of acclimation is indicated by only a small increase in pulse rate measured while performing mild exercise. In addition to enabling a user to become acclimated to higher altitudes, the method and apparatus disclosed in Applicant's parent application is useful for other purposes such as to increase endurance of competing athletes. That is, endurance during competition while breathing a certain PO.sub.2 will be enhanced by training while breathing a lower PO.sub.2.